The present invention relates to methods and compositions for modulating platelet aggregation, and methods and compositions for treating a disease or disorder associated with platelet aggregation in a subject, comprising administering a single chain TREM-like transcript-1 (TLT-1) antibody, or a functional fragment or variant thereof, in an amount effective to modulate platelet aggregation.
The triggering receptors expressed on myeloid cells (TREMs) are an emerging family of activating receptors expressed on various cells of the myeloid lineage (Bouchon, A. et al. (2000) J. Immunol. 164:4991-4995; Bouchon, A. et al. (2001) J. Exp. Med. 194:1111-1122; Daws, M. R. et al. (2001) Eur. J. Immunol. 31:783-791; Chung, D. H. et al. (2002) Eur. J. Immunol. 32:59-66). The TREMs represent a loose cluster (150 kb) on mouse chromosome 17, and the cluster's genomic organization is highly conserved on human chromosome 6. Although the family members possess only 30% amino acid identity, each member consists of a leader sequence, single V-set Ig domain, short cytoplasmic tail, and transmembrane domain containing a positively charged residue, suggesting interaction with a signaling polypeptide (Daws, M. R. et al. (2001) Eur. J. Immunol. 31:783-791; Chung, D. H. et al. (2002) Eur. J. Immunol. 32:59-66). Biochemical analysis has demonstrated that of the four TREM sequences described to date, TREMs 1, 2, and 3 associate with the activating signaling chain DAP 12, and TREM-4 is predicted to as well (Bouchon, A. et al. (2000) J. Immunol. 164:4991-4995; Bouchon, A. et al. (2001) J. Exp. Med. 194:1111-1122; Daws, M. R. et al. (2001) Eur. J. Immunol. 31:783-791; Chung, D. H. et al. (2002) Eur. J. Immunol. 32:59-66; Bouchon, A. et al. (2001) Nature 410:1103-1107). Bouchon et al. uncovered the importance of this family in the regulation of multiple facets of the immune response (Bouchon, A. et al. (2000) J. Immunol. 164:4991-4995; Bouchon, A. et al. (2001) J. Exp. Med. 194:1111-1122; Bouchon, A. et al. (2001) Nature 410:1103-1107). These studies defined TREM11 as an important mediator of septic shock (Bouchon, A. et al. (2000) J. Immunol. 164:4991-4995; Bouchon, A. et al. (2001) Nature 410:1103-1107; Nathan, C. and Ding, A. (2001) Nat. Med. 7:530-532; Cohen, J. (2001) Lancet 358:776-778), and TREM-2 as playing a unique role in dendritic cell maturation and, therefore, T-cell priming (Bouchon, A. et al. (2001) J. Exp. Med. 194:1111-1122; Bachmann, M. F. (2002) Trends Immunol. 23:10).
Platelets, also referred to as “blood platelets” or “peripheral blood platelets,” are small cells that lack a nucleus, but have a highly organized cytoskeleton, unique cell-surface receptors, and specialized secretory granules. Human blood contains nearly a trillion platelets, which respond to blood vessel injury by changing shape, secreting granule contents, and aggregation (Italiano, J. E., Jr. et al. (1999) J. Cell Biol. 147:1299-1312). These responses cause blood clotting to aid repair of injury and stop bleeding, but can also cause unwanted clots that lead to tissue ischemia and/or infarction, including stroke and heart attack. Platelets are produced through the terminal differentiation of megakaryocytes. Each mature megakaryocyte produces and releases hundreds of platelets into circulation (Kaufinan et al. (1965) Blood 26:720-728; Harker and Finch (1969) J. Clin. Invest. 48:963-974; and Trowbridge et al. (1984) Clin. Phys. Physiol. Meas. 5:145-156). Megakaryocytes, which make up about <0.1% of all cells in the bone marrow (Italiano et al. (1999) supra), are polyploid cells whose size and DNA content correlate directly with the circulating platelet mass (Ebbe and Stohlman (1965) Blood 26:20-34). Mature megakaryocytes assemble a unique set of organelles, including alpha granules, dense bodies, and an extensive system of internal membranes (Shivdasani, R. A. (2001) Stem Cells 19:397-407). Differentiated megakaryocytes extrude long cytoplasmic processes (“proplatelets”) that serve as the immediate precursors of circulating platelets (Choi, E. S. et al. (1995) Blood 85:402-413; Cramer, E. M. et al. (1997) Blood 89:2336-2346; Norol, F. et al. (1998) Blood 91:830-843). Megakaryocyte and platelet differentiation is controlled by a number of transcription factors, including GATA-1, FOG-1, and NF-E2 (Shivdasani et al. (2001) supra), as well as factors such as thrombopoietin.
Platelets play a crucial role in the mortality associated with cardiovascular disease (CVD) and therefore are a primary target for therapeutic intervention. Platelets are believed to assist in the advancement of CVD (Ruggeri Z M. Nat Med 2002; 8: 1227-34.), and it is estimated that 50-60% of sudden coronary death cases are caused by ruptured plaques consisting largely of platelets and fibrin (Burke A P, et al. N Engl J Med 1997; 336: 1276-82; Virmani R, et al. Arterioscler Thromb Vasc Biol 2000; 20: 1262-75). Errant platelet-mediated thrombosis is a common and life-threatening disease in the United State and through-out the world, and carries with it high mortality rates. To improve patient outcomes, drugs targeting platelet agonists are commonly used. Current efforts in anti-platelet therapy focus on separating the haemostatic function of platelets from their thrombotic nature (Phillips D R, et al. J Thromb Haemost 2005; 3: 1577-89; Nieswandt B, Aktas B, Moers A, Sachs U J. Platelets in atherothrombosis: lessons from mouse models. J Thromb Haemost 2005; 3: 1725-36). The new generation of anti-platelet therapies target specific activation pathways. Examples are clopidogrel, which inhibits platelet activation through the irreversible inhibition of the P2Y12 receptor (A randomised, blinded, trial of clopidogrel versus aspirin in patients at risk of ischaemic events (CAPRIE) CAPRIE Steering Committee. Lancet 1996; 348: 1329-39) and abciximab, a monoclonal F(ab′)2 fragment that target the platelet glycoprotein (GP) IIb/IIIa (Popma J J, et al. J Invasive Cardiol 1994; 6 Suppl A: 19A-28A; Genetta T B, et al. Ann Pharmacother 1996; 30: 251-7.). Although these therapies have shown partial efficacy and side effects, they demonstrate the utility of platelet membrane receptors as a new class of therapeutic targets for the regulation of platelet functions.
Thus, intervention with TLT-1 may have significant impact on managing and treating a range of diseases. Given the importance of platelets in blood clotting and wound healing, as well as their involvement in many disorders such as stroke and heart disease, and in sepsis and septic shock, there exists a need in the art for agents and methods that can modulate platelet aggregation and/or function.
Citation or identification of any document in this application is not an admission that such document is available as prior art to the present invention.